Britain's Prince Charles is driven by carriage from Buckingham Palace to the Houses of Parliament during the State Opening of Parliament in central London, Britain, May 27, 2015.Peter Nicholls

LONDON (Reuters) - The British government has released more letters penned by heir-to-the-throne Prince Charles to ministers expressing concern over issues ranging from climate change to public health, which have led to criticism he is meddling in politics.

The 17 letters to and from the prince or his aides between 2007 and 2009 reveal Charles raising matters such as affordable rural housing, the quality of food in hospitals and the preservation of historic buildings such as huts in the Antarctic used by British explorers Robert Scott and Ernest Shackleton.

Last month, the government disclosed 27 letters - dubbed the 'black spider memos' because of the prince's scrawled handwriting - after losing a decade-long battle to prevent publication on the grounds they might cast doubt over the future king's political neutrality.

Under Britain's unwritten constitution, the royal family is supposed to remain above politics, and Queen Elizabeth has kept her opinions to herself during her 63-year reign.

Critics accuse the prince of interfering and putting pressure on ministers while supporters say he is merely raising issues which he and many ordinary Britons care about.

"In all these cases, The Prince of Wales is raising issues of public concern, and trying to find practical ways to address the issues," his office said in a statement on Thursday.

In one of the latest and final batch of letters to be publicized, Charles lobbies for complementary medicine to be integrated alongside conventional state-run healthcare services. here

In another, he says that the failure to carry out regeneration work in cases of two decaying buildings in Wales and central England "makes me weep".

Republic, a group that campaigns for the abolition of the monarchy, has called for an investigation into Charles's lobbying and said if he wanted to influence politics, he should stand for election.

"Charles is deliberately trying to change government policy," it said on its Twitter website. "The voters have a right to know when and what impact he's having."